1. Field of the Invention
This invention relates to a plasma processing apparatus used for processing of a sample such as wafer by use of plasma in a reduced pressure atmosphere.
2. Related Background Art
For example, conventional plasma processing apparatus for processing a sample such as wafer by use of plasma in a reduced pressure atmosphere are disclosed in JP-A (Unexamined patent publication) No. H9-7988 and JP-A No. H11-330044. These inventions describe insulation processing on the surface or inner wall of component parts such as grounding member in a chamber. In detail, the insulation processing with aluminum-alumite is applied on an grounding surface of the conductive grounding member consisting of aluminum alloy. In other words, a ring provided on the outside of a sample table in a processing chamber that is used for grounding consists of conductive grounding material, and the insulation processing is applied on the surface. An alumite film is formed on the surface of the ring consisting of aluminum alloy by means of anodizing technique.
Furthermore, JP-A No. H8-250469 proposes a technique in which carbon silicate (SiC) is used for grounding.
The above-mentioned conventional techniques insufficiently address the surface thinning of the insulation-processed layer due to etching gas or plasma. In detail, the thinning of the insulation-processed layer and substrate itself due to plasma causes diffusion of impurities contained in the material and the diffusion adversely affects the quality of a wafer sample. The thinning of the insulation-processed layer due to plasma affects electrically to thereby change the state of the plasma. Since components such as grounding member are exposed to plasma, the components should be inevitably replaced frequently as expendable components, in the conventional plasma processing apparatus.
In detail, because an alumite film on the ring surface is as thin as 10 to 50 μm, the alumite film is thinned gradually during exposing to plasma, and finally aluminum alloy, which is mother material of the ring, is exposed to plasma. If aluminum alloy is exposed continuously, the exposure adversely affects the plasma electrically, and the ring is thinned faster than alumite film because the ring is less corrosion resistant than alumite film. The exposure causes diffusion of impurities and aluminum itself as foreign matter in plasma, and adversely affects devices. To avoid such problem, when an alumite film is thinned exhaustively, it is required to replace the thinned ring with a new ring immediately, because the ring is expendable.
Furthermore, even though ceramic such as carbon silicate (SiC) that is resistant to plasma is used as component parts, the life is short, and it is required to replace it frequently. The reason is that silicon (Si) and carbon (C) that are used as the material of the component parts are materials that are accessible to thinning due to plasma for wafer processing, and that are accessible to chemical reaction due to exposure to plasma.